1. Field of the Invention
The present invention relates to a method of marking liquids using at least two markers, wherein said markers absorb in the 600-1200 nm region of the spectrum and reemit fluorescent light and the absorption range of at least one marker overlaps with the absorption range of at least one other marker.
2. Description of the Related Art
The present invention further relates to a method for detecting markers in liquids marked by the method of the invention, which comprises using light sources which emit radiation in the absorption ranges of said markers and detecting the fluorescent light reemitted by said markers, at least one of said light sources emitting radiation in the overlapping absorption range of at least one marker with that of at least one other marker and the number of light sources being less than or equal to the number of markers.
The present invention further relates to liquids marked by the method of the invention.
It is frequently necessary to mark, or tag, liquids to allow their subsequent detection, for example in use, by means of suitable methods. This makes it possible, for example, to differentiate heating oil, which normally enjoys a favorable tax status, from the generally more highly taxed diesel oil, or to tag liquid product streams in large industrial plants, for example petroleum refineries, and to trace them thereby.
If the marking of the liquids is to be invisible to the human eye, it is necessary to resort to the use of markers which absorb and/or emit radiation outside the visible region of the spectrum. Owing to the extreme sensitivity of detection and the attendant possibility of achieving reliable marking with low levels of added marker, pride of place belongs here especially to markers which reemit the absorbed radiation as fluorescent light. This emitted radiation generally has a lower frequency than the absorbed radiation (STOKES radiation), less frequently the same frequency (resonance fluorescence) or even a higher frequency (ANTI-STOKES radiation).
Great economic importance attaches to the marking of hydrocarbons and hydrocarbon mixtures (e.g., various grades of diesel and gasoline motor fuels and of other mineral oils). Since these liquids usually themselves have high absorption and/or fluorescence in the region of the spectrum below about 600 nm, its is not surprising that the markers used absorb and/or fluoresce above about 600 nm.
Ideally, compounds useful as markers should therefore possess the following basic properties:
strong absorption in the 600-1200 nm region of the spectrum, PA1 little or no absorption/fluorescence in the visible region of the spectrum, PA1 strong emission of fluorescent light in the region of the spectrum which extends from about 600 to about 1200 nm, PA1 give detectable emission levels of fluorescence when added to the liquid in question at less than 1 ppm by weight, and PA1 adequate solubility in the liquid to be marked. PA1 miscibility with other markers and any other additives present (the marked and possibly additived liquids should also be miscible with each other), PA1 adequate stability to the action of external conditions, e.g., temperature, light, moisture, etc., alone and dissolved in the liquid to be marked, PA1 not be harmful to the environment in which they are used, e.g., internal combustion engines, storage tanks, etc., and PA1 be both toxicologically and ecologically safe. PA1 said markers absorb in the 600-1200 nm region of the spectrum and reemit fluorescent light and PA1 the absorption range of at least one marker overlaps with the absorption range of at least one other marker. PA1 Me.sup.1 is two hydrogens, two lithiums, magnesium, zinc, copper, nickel, VO, TiO, AlCl, AlO--C.sub.1 -C.sub.20 -alkyl, AlNH--C.sub.1 -C.sub.20 -alkyl, AlN(C.sub.1 -C.sub.20 -alkyl).sub.2, AlO--C.sub.6 -C.sub.20 -aryl, Al--NH--C.sub.6 -C.sub.20 -aryl or AlN(C.sub.6 -C.sub.20 -aryl).sub.2, AlN--Het, where N--Het is a heterocyclic, saturated or unsaturated five-, six- or seven-membered ring which, as well as at least one nitrogen atom, can contain one or two further nitrogen atoms and/or a further oxygen or sulfur atom in the ring, which is unsubstituted or singly to triply substituted by C.sub.1 -C.sub.4 -alkyl, phenyl, benzyl or phenylethyl and which is attached to the aluminum atom via a (or the) ring nitrogen atom, or Si(OH).sub.2, PA1 at least 4 of the radicals R.sup.1 to R.sup.16 are each independently a radical of the formula W--X.sup.1, where W is a chemical bond, oxygen, sulfur, imino, C.sub.1 -C.sub.4 -alkylimino or phenylimino and X.sup.1 is C.sub.1 -C.sub.20 -alkyl or C.sub.3 -C.sub.10 -cycloalkyl with or without interruption by from 1 to 4 oxygen atoms in ether function and with or without phenyl substitution, adamantyl or substituted or unsubstituted phenyl, heterocyclic, saturated five-, six- or seven-membered rings which can additionally contain one or two further nitrogen atoms and/or one further oxygen or sulfur atom in the ring, which are unsubstituted or singly to triply substituted by C.sub.1 -C.sub.4 -alkyl, phenyl, benzyl or phenylethyl and which are attached to the benzene ring via a (or the) ring nitrogen atom, and PA1 any remaining radicals R.sup.1 to R.sup.16 are each hydrogen, halogen, hydroxysulfonyl or C.sub.1 -C.sub.4 -dialkylsulfamoyl. PA1 R.sup.17 and R.sup.18 or R.sup.18 and R.sup.19 or R.sup.19 and R.sup.20 are paired off to form a radical of the formula X.sup.2 --C.sub.2 H.sub.4 --X.sup.3, where one of X.sup.2 and X.sup.3 is oxygen and the other is imino or C.sub.1 -C.sub.4 -alkylimino, and PA1 R.sup.19 and R.sup.20 or R.sup.17 and R.sup.20 or R.sup.17 and R.sup.18 are each independently hydrogen or halogen, and PA1 Me.sup.1 is as defined above. PA1 Y.sup.1, Y.sup.2, Y.sup.3, Y.sup.4, Y.sup.5, Y.sup.6, Y.sup.7 and Y.sup.8 are each independently hydrogen, hydroxyl, C.sub.1 -C.sub.20 -alkyl, C.sub.3 -C.sub.10 -cycloalkyl or C.sub.1 -C.sub.20 -alkoxy, where the alkyl groups may each be interrupted by from 1 to 4 oxygen atoms in ether function and may be phenyl-substituted, heterocyclic, saturated five-, six- or seven-membered rings which can additionally contain one or two further nitrogen atoms and/or a further oxygen or sulfur atom in the ring, which are unsubstituted or singly to triply substituted by C.sub.1 -C.sub.4 -alkyl, phenyl, benzyl or phenylethyl and which are attached to the benzene ring via a (or the) ring nitrogen atom, PA1 Y.sup.9, Y.sup.10, Y.sup.11 and Y.sup.12 are each independently hydrogen, C.sub.1 -C.sub.20 -alkyl or C.sub.1 -C.sub.20 -alkoxy, where the alkyl groups may each be interrupted by from 1 to 4 oxygen atoms in ether function, halogen, hydroxysulfonyl or C.sub.1 -C.sub.4 -dialkylsulfamoyl, and PA1 Me.sup.2 is Me.sup.1 or is the radical ##STR4## PA1 Y.sup.17 and Y.sup.18 are each independently hydroxyl, C.sub.1 -C.sub.20 -alkoxy, C.sub.1 -C.sub.20 -alkyl, C.sub.2 -C.sub.20 -alkenyl, C.sub.3 -C.sub.20 -alkenyloxy or a radical of the formula ##STR5## PA1 where Y.sup.19 is C.sub.1 -C.sub.20 -alkyl, C.sub.2 -C.sub.20 -alkenyl or C.sub.4 -C.sub.20 -alkadienyl and Y.sup.20 and Y.sup.21 are each independently C.sub.1 -C.sub.12 -alkyl, C.sub.2 -C.sub.12 -alkenyl or the abovementioned radical OY.sup.19. PA1 L.sup.1, L.sup.2, L.sup.3 and L.sup.4 are each independently C.sub.1 -C.sub.20 -alkyl, with or without interruption by from 1 to 4 oxygen atoms in ether function, phenyl, C.sub.1 -C.sub.20 -alkylphenyl, C.sub.1 -C.sub.20 -alkoxyphenyl, where the alkyl groups may each be interrupted by from 1 to 4 oxygen atoms in ether function, or L.sup.1 and L.sup.2 and/or L.sup.3 and L.sup.4 are in each case together the radical of the formula ##STR7## PA1 Z.sup.1, Z.sup.2, Z.sup.3 and Z.sup.4 are each independently C.sub.1 -C.sub.20 -alkyl, with or without interruption by from 1 to 4 oxygen atoms in ether function, C.sub.1 -C.sub.20 -alkanoyl or a radical of the formula ##STR9## PA1 A.sup.n.crclbar. is the equivalent of an anion. PA1 E.sup.1 and E.sup.2 are each independently oxygen, sulfur, imino or a radical of the formula EQU --C(CH.sub.3).sub.2 -- or --CH.dbd.CH--, PA1 D is a radical of the formula ##STR11## PA1 Q.sup.1 and Q.sup.2 are each independently phenyl, C.sub.5 -C.sub.7 -cycloalkyl, C.sub.1 -C.sub.12 -alkyl with or without interruption by from 1 to 3 oxygen atoms in ether function and with or without substitution by hydroxyl, chlorine, bromine, carboxyl, C.sub.1 -C.sub.4 -alkoxycarbonyl, acryloyloxy, methacryloyloxy, hydroxysulfonyl, C.sub.1 -C.sub.7 -alkanoylamino, C.sub.1 -C.sub.6 -alkylcarbamoyl, C.sub.1 -C.sub.6 -alkylcarbamoyloxy or a radical of the formula G.sup..sym. (K).sub.3, where G is nitrogen or phosphorus and K is phenyl, C.sub.5 -C.sub.7 -cycloalkyl or C.sub.1 -C.sub.12 -alkyl, PA1 A.sup.n.crclbar. is the equivalent of an anion, and PA1 n is 1, 2 or 3. PA1 J is C.sub.1 -C.sub.12 -alkylene, PA1 T.sup.2, T.sup.3, T.sup.4 and T.sup.5 are each independently hydrogen or C.sub.1 -C.sub.12 -alkyl, with or without halogen, amino, C.sub.1 -C.sub.12 -alkoxy, phenyl, substituted phenyl, carboxyl, C.sub.1 -C.sub.12 -alkoxycarbonyl or cyano substitution, PA1 Y.sup.1, Y.sup.2, Y.sup.3, Y.sup.4, Y.sup.5, Y.sup.6, Y.sup.7 and Y.sup.8 are each independently hydrogen, hydroxyl, C.sub.1 -C.sub.4 -alkyl or C.sub.1 -C.sub.20 -alkoxy and PA1 Me.sup.2 is Me.sup.1 or the radical ##STR15## PA1 alcohols, such as methanol, ethanol, propanol, isopropanol, butanol, isobutanol, sec-butanol, pentanol, isopentanol, neopentanol or hexanol, PA1 glycols, such as 1,2-ethylene glycol, 1,2- or 1,3-propylene glycol, 1,2-, 2,3- or 1,4-butylene glycol, di- or triethylene glycol or di- or tripropylene glycol, PA1 ethers, such as methyl tert-butyl ether, 1,2-ethylene glycol monomethyl ether, 1,2-ethylene glycol dimethyl ether, 1,2-ethylene glycol monoethyl ether, 1,2-ethylene glycol diethyl ether, 3-methoxypropanol, 3-isopropoxypropanol, tetrahydrofuran or dioxane, PA1 ketones, such as acetone, methyl ethyl ketone or diacetone alcohol, PA1 esters, such as methyl acetate, ethyl acetate, propyl acetate or butyl acetate, PA1 aliphatic or aromatic hydrocarbons such as pentane, hexane, heptane, octane, isooctane, petroleum ether, toluene, xylene, ethyl benzene, tetralin, decalin, dimethylnaphthalene, white spirit, PA1 natural oils, such as olive oil, soybean oil or sunflower oil, or natural or synthetic engine, hydraulic or gear oils, for example automotive vehicle engine oil or sewing machine oil, or brake fluids PA1 and mineral oils, such as gasoline, kerosine, diesel oil or heating oil. PA1 A) All adjacent wavelength intervals L.mu. and L(.mu.+1) form non-empty overlaps (intersections); all nonadjacent wavelength intervals L.mu. and L.nu. (.nu.&gt;.mu.+1) have no "higher" overlaps (intersections), i.e., form empty sets in each case, viz: EQU L.mu..nu..noteq.{.O slashed.} PA1 a sample cuvette which contains the marked liquid, PA1 an excitation unit (A) comprising: PA1 .alpha..sub.1) a light source, usually equipped with collimator optics, and PA1 .alpha..sub.2) usually a plane mirror which is positioned opposite to the light source on that side of the sample cuvette which is remote from the light source, and reflects the transmitted radiation to increase the intensity irradiated into the sample, PA1 a detection unit (D) comprising: PA1 .delta..sub.1) a photodetector (usually provided with collimator optics) in front of which there are usually positioned optical filters (e.g., cutoff or interference filters) and optionally NIR polarizers and which is disposed in such a way that the fluorescent light reemitted in its direction is incident (or imaged) thereon and detected, and PA1 .delta..sub.2) usually a concave mirror which is positioned opposite the photodetector on that side of the sample cuvette which is remote from the photodetector, and reflects the fluorescent light reemitted in the opposite direction (away from the photodetector) and hence serves to enhance the sensitivity of detection. PA1 I) in the same sample volume or PA1 II) in different sample volumes. PA1 I.1) A.mu..sub.1.nu..sub.1.omega..sub.1 /D1, A.mu..sub.2.nu..sub.2.omega..sub.2 /D2, . . . , A.mu..sub.n-1.nu..sub.n-1.omega..sub.n-1 /Dn-1,A.mu..sub.n.nu..sub.n.omega..sub.n /Dn (the n markers M.mu. are each excited in the overlaps L.mu..nu..omega. by their corresponding units A.mu..nu..omega. and the fluorescent emissions of the markers M.mu. are each detected by the units D.mu.). PA1 I.2) A/D1, A/D2, . . . , A/Dn-1,A/Dn (all n markers M.mu. are simultaneously excited by a "polychromatic" light source and detected by means of their respective detection channel D.mu.). PA1 I.3) A.mu..sub.1.nu..sub.1.omega..sub.1 /D, A.mu..sub.2.nu..sub.2.omega..sub.2 /D, . . . , A.mu..sub.n-1.nu..sub.n-1.omega..sub.n-1 /D, A.mu..sub.n.nu..sub.n.omega..sub.n /D (the n markers M.mu. are each excited in the overlaps L.mu..nu..omega. by the corresponding units A.mu..nu..omega. and the fluorescent emissions of the markers M.mu. are each detected by the units D.mu.). PA1 I.4) A(.mu..sub.1.nu..sub.1.omega..sub.1, .mu..sub.2.nu..sub.2.omega..sub.2, . . . ,.mu..sub.n-1.nu..sub.n-1.omega..sub.n-1,.mu..sub.n.nu..sub.n.omega..sub. n)/D1, A(.mu..sub.1.nu..sub.1.omega..sub.1, .mu..sub.2.nu..sub.2.omega..sub.2, . . . ,.mu..sub.n-1.nu..sub.n-1.omega..sub.n-1, .mu..sub.n.nu..sub.n.omega..sub.n)/D2, . . . , A(.mu..sub.1.nu..sub.1.omega..sub.1, .mu..sub.2.nu..sub.2.omega..sub.2, . . . ,.mu..sub.n-1.nu..sub.n-1.omega..sub.n-1, .mu..sub.n.nu..sub.n.omega..sub.n)/Dn-1, A(.mu..sub.1.nu..sub.1.omega..sub.1, .mu..sub.2.nu..sub.2.omega..sub.2, . . . ,.mu..sub.n-1.nu..sub.n-1.omega..sub.n-1, .mu..sub.n.nu..sub.n.omega..sub.n)/Dn (the n markers M.mu. are each excited in the overlaps L.mu..nu..omega. and detected by means of their respective detection channel D.mu.). PA1 I.5) A.mu..sub.1.nu..sub.1.omega..sub.1 /D(1,2, . . . ,n-1,n), A.mu..sub.2.nu..sub.2.omega..sub.2 /D(1,2, . . . ,n-1,n), . . . , A.mu..sub.n-1.nu..sub.n-1.omega..sub.n-1 /D(1,2, . . . ,n-1,n), A.mu..sub.n.nu..sub.n.omega..sub.n /D(1,2, . . . ,n-1,n) (the n markers M.mu. are each excited in the overlaps L.mu..nu..omega. by their corresponding unit A.mu..nu..omega. and detected). PA1 I.6) A(.mu..sub.1.nu..sub.1.omega..sub.1, .mu..sub.2.nu..sub.2.omega..sub.2, . . . ,.mu..sub.n-1.nu..sub.n-1.omega..sub.n-1, .mu..sub.n.nu..sub.n.omega..sub.n)/D(1,2, . . . ,n-1,n) (the n markers M.mu. are each excited in the overlaps L.mu..nu..omega. and detected). PA1 I.7) A.mu..sub.1.nu..sub.1.omega..sub.1 /A.mu..sub.2.nu..sub.2.omega..sub.2 / . . . /A.mu..sub.n-1.nu..sub.n-1.omega..sub.n-1 /A.mu..sub.n.nu..sub.n.omega..sub.n /D1/D2/ . . . /Dn-1/Dn (the n markers M.mu. are simultaneously excited in the regions of overlap by the corresponding units A.mu. and simultaneously detected by the units D.mu.). PA1 II.1) A1/D1, A2/D2, . . . , An-1/Dn-1,An/Dn (the n markers M.mu. are each excited in the regions of overlap L.mu..nu..omega. by the corresponding units A.mu..nu..omega. and detected by the respective units D.mu.). PA1 II.2) A.mu..sub.1.nu..sub.1.omega..sub.1 /D, A.mu..sub.1.nu..sub.1.omega..sub.1 /D, . . . , A.mu..sub.n-1.nu..sub.n-1.omega..sub.n-n /D (the n markers M.mu. are each excited in the regions of overlap by the corresponding unit A.mu..nu..omega. and detected using a detection unit D, for example a multiwavelength detector. PA1 II.3) A.mu..sub.1.nu..sub.1.omega..sub.1 /D(1,2, . . . , n-1,n), A.mu..sub.2.nu..sub.2.omega..sub.2 /D(1,2, . . . , n-1,n), . . . , A.mu..sub.n-1.nu..sub.n-1.omega..sub.n-1 /D(1,2 . . . ,n-1,n), A.mu..sub.n.nu..sub.n.omega..sub.n /D(1,2, . . . , n-1,n) (the n markers M.mu. are each excited in the regions of overlap L.mu..nu..omega. by the corresponding units A.mu..nu..omega. and detected). PA1 II.4) A.mu..sub.1.nu..sub.1.omega..sub.1 /A.mu..sub.2.nu..sub.2.omega..sub.2 / . . . /A.mu..sub.n-1.nu..sub.n-1.omega..sub.n-1 /A.mu..sub.n.nu..sub.n.omega..sub.n /D1/D2/ . . . /Dn-1/Dn (the n markers are simultaneously excited in the regions of overlap L.mu..nu..omega. by the corresponding units A.mu..nu..omega. and simultaneously detected by the units D.mu.).
In addition, depending on the specific application requirements, compounds useful as markers may have to satisfy one or more of the following requirements:
WO 94/02570 describes marking liquids by using markers having their absorption maximum within the range from 600 to 1200 nm and/or a fluorescence maximum within the range from 620 to 1200 nm selected from the group consisting of the metal-free and metal-containing phthalocyanines, the metal-free and metal-containing naphthalocyanines, the nickel-dithiolene complexes, the aminium compounds of aromatic amines, the methine dyes and the azulenesquaric acid dyes. It further describes a method essentially comprising detecting the fluorescent light of the marker present in the liquid, which marker absorbs radiation in the stated region of the spectrum. The cited reference also describes a detector for the marker. However, the simultaneous use of two or more markers is not explicitly mentioned.
U.S. Pat. No. 5,525,516 likewise describes a method for marking mineral oils with compounds which fluoresce in the NIR region. Substituted phthalocyanines, substituted naphthalocyanines and squaric or croconic acid derivatives are used as such markers. This U.S. Patent states in the description part (column 3, lines 35 to 40) that it is also within the scope of the invention described therein to mark one or more mineral oils not just with one, but also with two or more compounds which fluoresce in the IR region. It is further stated in this passage that these two or more compounds are selected so that they absorb IR radiation and/or reemit fluorescent light at wavelengths different enough from each other so as not to interfere with individual detection. Using the (then) state of the art detection equipment it is believed (column 4, lines 25 to 28) that such differences in absorption/fluorescence of as little as 20 nm in wavelength can be discerned. This reference explicitly rules out using markers having overlapping regions of absorption. What is more, it is pointed out (column 3, lines 41 to 44) that this or these fluorescent compound(s) should preferably absorb at wavelengths below 850 nm, since mineral oils absorb above this wavelength.
U.S. Pat. No. 5,525,516 further claims a method for identifying mineral oils which have been marked with one or more markers. The marked mineral oil, or the markers incorporated therein, are exposed to electromagnetic radiation within the range (absorption range) of 670-850 nm. But beyond that no further information is provided as to how to proceed when mineral oils have been marked with more than one marker.
U.S. Pat. No. 5,710,046 describes a method for tagging gasoline, again essentially by detecting an essentially metal-free fluorescent dye dissolved in the gasoline. An appropriately tagged gasoline is excited with radiation from a wavelength band of 600 to 2500 nm, the fluorescent light emitted by the dye in the wavelength band from about 600 to 2500 nm is detected, and the resulting detection signal is used to identify the tagged sample. This reference further describes at length the construction of a detector for detecting the fluorescent dyes in the tagged gasoline samples. However, the use of a plurality of markers (dyes) is not discussed.
If liquids, for example hydrocarbons and hydrocarbon mixtures (e.g., diesel and gasoline fuels and other mineral oils), from different sources or different manufacturers are to be marked, a multiplicity of different markers are required if only one marker is used per liquid. These different markers have to be sufficiently different in their absorption and/or fluorescence characteristics in order that the liquids may be identified with regard to their provenience and/or producer. Moreover, marking liquids with just one marker makes it easier for others to falsify unmarked liquids by adding the appropriate marker. This is of immense significance when chemically and qualitatively equivalent liquids carry different fiscal duties. An example are heating oil and diesel fuel.